instmctions): Pathogenic mechanisms undertying the development of respiratory tularemia, a zoonotic disease caused by the facultative intracellular bacterium Francisella tularensis (Ft), are incompletely defined. However, using a mouse model of infection we previously reported that recognition of the live vaccine strain (LVS) of Ft subspecies (spp) holarctica via Toll-like receptor 2 (TLR2) contributes to host resistance to infection. Most TLRs are expressed on the host cell surface and are involved in the extracellular recognition of both microbe-expressed molecular structures (MEMS) and endogenous "danger" signals. Members of the nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family can detect such molecules within the host cell cytoplasm and thus act as the intracellular equivalent of TLRs. Very little is known, however, regarding how extra- and intracellular recognition of pathogens influences the host cell's permissiveness for cytosolic replication of Ft or the development of protective immunity. Specifically, whether antibody bound to Ft alters innate recognition by TLR2 or NLR and thereby the adaptive/protective immune response is not known. Changes in the pathogen's capacity to resist redox-mediated host defenses could have similar effects on disease outcome, as well as the ability to generate adaptive/protective immunity. Thus, we hypothesize that signals transduced via TLR2 modulate NLR-mediated intracellular recognition of Ft thereby influencing bacterial survival and the host inflammatory response; further, these processes may be impacted by antibody opsonization of Ft and the antioxidant potential of Ft. This hypothesis will be tested by 1) characterizing the role of TLR2 signaling and inflammasome activation on host cell response and Ft intracellular growth, 2) establishing the molecular requirements for Ft-induced inflammasome activation, and 3) establishing the impact of mAb bound to Ft or Ft antioxidant mutants on TLR2/NLR signaling during the innate immune (inductive) phase ofthe anti-Ft immune response. RELEVANCE (See instructions): The overarching goal of this proposal is to understand the cellular and molecular features of TLR2/NLR- mediated responses, how these processes are coordinated with the host's ability to restrain bacterial growth, how these responses contribute to resisting pathogenic challenge at the level of the whole organism, and how mAb bound to Ft, inactivated Ft, Ft antioxidant mutants influences the above events.